Technical Field
The present invention relates to a high-power semiconductor laser that uses a vertical cavity surface emitting laser (VCSEL) as a light source, and also to an optical convergence method for the high-power semiconductor laser, and belongs to the field of semiconductor laser technologies.
Related Art
Over the past twenty years, in the field of high-power semiconductor lasers, GaAs material-based edge-emitting semiconductor lasers have always been dominant, and have been widely applied to fields such as industry, medical treatment, and scientific research. However, the edge-emitting semiconductor lasers have fatal defects. Although an expected life of service of an edge-emitting semiconductor laser is up to tens of thousands of hours, the catastrophic optical damage probability of the edge-emitting semiconductor laser in a pulse status is extremely great, which seriously affects the life of service. Therefore, an actual life of service of the edge-emitting semiconductor laser is far from reaching the ideal expected life of service. Therefore, a new semiconductor laser applicable to the industrial field needs to be provided.
In the field of semiconductor lasers, lasers may be grouped into two types: VCSELs and edge-emitting semiconductor lasers according to a relationship between a light emitting direction and an epitaxial wafer plane where a laser chip is located. A light emitting direction of a VCSEL is perpendicular to an epitaxial wafer direction, and light is emitted from a top surface of a reaction region. A light emitting direction of an edge-emitting semiconductor laser is parallel to an epitaxial wafer direction, and light is emitted from an edge of a reaction region. Refer to the schematic diagram shown in FIG. 1 for structures of the VCSEL and the edge-emitting semiconductor laser.
The edge-emitting semiconductor laser and the VCSEL respectively have the following features: the edge-emitting semiconductor laser is a linear light source, a divergence angle of the edge-emitting semiconductor laser in the vertical direction is extremely different from a divergence angle of the edge-emitting semiconductor laser in the horizontal direction (a full angle in the vertical direction is approximately 60 degrees to 70 degrees, and a full angle in the horizontal direction is approximately 7 degrees to 10 degrees), and far field intensity of the edge-emitting semiconductor laser is in Gaussian distribution; however, as shown in FIG. 2, the VCSEL is a circular light source, and has a relatively small divergence angle (a full angle of the divergence angle is approximately 15 degrees to 20 degrees), far field intensity of the VCSEL is in approximately flat top distribution, and energy is uniform. Therefore, as compared with the edge-emitting semiconductor laser, light rays emitted by the VCSEL are more easily converged, and energy distribution on a far field target object is uniform. In addition, as compared with the edge-emitting semiconductor laser, the VCSEL further has other advantages. For example, the VCSEL has a relatively high working temperature, a relatively long expected life of service, and a low fault rate, may further be packaged by using a process similar to an LED process, and has a low package process requirement. However, conventional VCSELs have always been ignored in the high-power market due to relatively low electro-optic efficiency and relatively poor optical brightness.
With the progress of technologies in recent years, a high-power output of the VCSEL similar to that of the edge-emitting semiconductor laser has been gradually implemented. Also, due to a unique structure of the VCSEL, there are multiple advantages in application of the VCSEL, for example, high reliability, high temperature resistance, uniform optical distribution, and high surface reflectivity. A brand new revolution will be brought to the field of semiconductor lasers if the VCSEL is improved to be gradually applied to some industrial application fields.
Refer to Table 1 for specific performance comparison between the VCSEL and the edge-emitting semiconductor laser.
TABLE 1Structural performance comparison between edge-emitting semiconductorlaser and VCSELEdge-emitting laser (singleIndexpoint or array)VCSEL (single point or array)Light emittingDirection of a plane where anPerpendicular to a plane wheredirectionepitaxial wafer is locatedan epitaxial wafer is locatedLight emitting regionLinear light source, or formedCircular light source, or formedhorizontal + vertical arrayarea arrayDivergence angleFull angle in a verticalFull angle of a divergence angledirection is approximately 60is approximately 15 degrees todegrees to 70 degrees20 degreesFull angle in a horizontalIn a circular symmetry structuredirection is approximately 7degrees to 10 degreesSurface reflectivityDepending on an arrayExtremely high reflectivity,package manner, generally low>99.5%Far field intensity atGaussian distributionApproximately flat topluminous pointsdistribution, and uniform energySpectral widthGenerally, >2.5 nmGenerally, <1 nmWavelength-temperature0.3 nm/C.<0.07 nm/C.driftWorking temperature<35 C. (industrial grade), <45 C.>80 C. even >100 C.(communication grade)Electro-optic50% to 60%, efficiency45% to 60%, slightly low, butefficiencyseriously decreases under highrelatively high efficiency cantemperaturestill be maintained under hightemperatureCatastrophic opticalExist, has extremely greatNot existdamageaffect on life of serviceExpected life of−10000 hours (industrialMore than hundreds of thousandsservicegrade), −50000 hoursof hours(communication grade)Fault rate (*FIT rate)Industrial grade FIT >1000,FIT <2, has extremely highcommunication grade FIT-500reliabilityPackage processHigh package technicalLow package technicalrequirementrequirement, similar to an LEDprocessNote:*FIT rate is the number of faults that occur in every 1 billion device working hours